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Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks
Journal of Alloys and Compounds xxx (xxxx) xxx
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Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks Jing Feng a, b, Zongbin Li a, *, Dong Li a, Bo Yang a, Lingwei Li c, **, Xiang Zhao a, Liang Zuo a a
Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang, 110819, PR China b State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200030, PR China c Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang, 110819, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 June 2019 Received in revised form 7 September 2019 Accepted 5 October 2019 Available online xxx
Achieving continuous dual-absorption peaks in ferromagnetic materials with micron-sized particles is quite challenging in designing the potential electromagnetic wave (EMW) absorbing materials. Here, we realize this effect in ball-milled Ni2MnGa microparticles and report their EMW absorbing properties for the first time. The as-milled Ni2MnGa/paraffin-bonded hybrids exhibit highly efficient EMW absorbing performance owing to the continuous dual-absorption peaks induced by enhanced dielectric loss and weakened magnetic loss associated with the permeability-to-permittivity energy transformation at the frequency of 2.0e18.0 GHz. The optimal EMW absorbing properties with the RLmin value up to 65.2 dB can be obtained at a frequency of ~14.4 GHz with a thickness of 2.90 mm. The effective absorption bandwidth with RL values less than 10 dB can reach 12.7 GHz through tuning the absorber thickness. It is demonstrated that Heusler-type NiMn-based alloys could be an attractive mono-component ferromagnetic absorber with highly efficient dual-absorption peaks. © 2019 Elsevier B.V. All rights reserved.
Keywords: Ni2MnGa Heusler alloy Electromagnetic absorption Dual-absorption peaks Ball milling
1. Introduction The wide applications of wireless communications and highfrequency electronic devices have given rise to significant electromagnetic wave pollution in our surroundings. To eliminate such detrimental effect, high-performance electromagnetic absorption materials (EMAMs), with the combination of broad bandwidth, light weight, thin thickness and good thermal and chemical stability, are highly desired [1e4]. In fact, the excellent electromagnetic absorbing performance of any EMAMs could mainly be achieved through improving the impedance matching associated with their intrinsic electromagnetic parameters of the complex permeability and permittivity (m0 , m00 , ε0 , ε00 ). Along this line, considerable efforts have been devoted to designing and fabricating diverse absorbers, e.g., magnetic, dielectric and magnetic-dielectric composites, to realize optimal electromagnetic wave (EMW) absorption. In recent years, some magnetic-dielectric nanocomposites such as Fe3O4/graphene [5], Ni/graphene [6], CuS/Ag2S
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (Z. Li), [email protected] (L. Li).
[7], are found to exhibit enhanced EMW absorbing properties, since the dual-absorption peaks enable broader bandwidth with respect to that of mono-component absorbent. Although the bonus of dualabsorption peaks in magnetic-dielectric nanocomposites has been well acknowledged, the complicated preparation processes and poor thermal and environmental stability impose strong constraints on their practical applications. Recently, it has been found that some ferromagnetic materials exhibit good EMW absorption properties at relatively high frequency, with the advantages in matching the electromagnetic parameters (m0 , m00 , ε0 , ε00 ) through tuning the composition, microstructure, particle size and morphology [8e15]. Especially, ferromagnetic Heusler-type NiMn-based alloys have attracted considerable attention in last twenty years, not only because of their unusual resonance behaviors [16,17], but also due to their multifunctional features, such as magnetic shape memory effect (MSME) [18e20], magnetocaloric effect (MCE) [21e24], magnetoresistance effect (MRE) [25], and elastocaloric effect [26,27]. Besides, our recent results show that the ferromagnetic Ni2þxMn1-xGa alloy particles also possess significant high-frequency EMW absorption performance [17], which enlarges the frontier of functional behaviors for these alloys. Unfortunately, the narrow effective
https://doi.org/10.1016/j.jallcom.2019.152588 0925-8388/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: J. Feng et al., Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152588
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absorption bandwidth still represents a substantial drawback in view of the potential applications. In this regard, exploring dualabsorption peaks is a feasible strategy to extend the bandwidth. Although the dual-absorption peaks have been experimentally observed in the shell@core nanocomposites [28,29], the realization of dual-absorption peaks in ferromagnetic particles, especially the newly developed NiMn-based alloys, is still a primary challenge. In this work, we report the enhanced EMW absorbing performance due to the continuous dual-absorption peaks in Ni2MnGa microparticles prepared by ball-milling. It is shown that the microparticles with milling time of 16 h exhibits the optimal EMW absorbing performance, where the RLmin value of 65.2 dB is achieved at ~14.4 GHz with a thickness of 2.90 mm. Moreover, the effective absorption bandwidth with RL value less than 10 dB can reach ~12.7 GHz with a thickness range of 1.65e5.00 mm, due to the continuous dual-absorption peaks induced by enhanced dielectric resonance and weakened magnetic anti-resonance. The present work is the first report on the continuous dual-absorption peaks in NiMn-based alloy microparticles. It is demonstrated that the mechanical ball-milling is an efficient processing route to tune the EMW absorption performance for the NiMn-based alloys. 2. Experimental Stoichiometric Ni2MnGa polycrystalline alloy was prepared by arc-melting in argon atmosphere with high-purity raw elements nickel (4 N), manganese (3 N), and gallium (4 N). In order to achieve a good composition homogenization, the as-cast ingot was then encapsulated in a vacuum quartz tube and annealed at 1173 K for 36 h, followed by quenching into water. The homogenized ingot was mechanically crushed and ground into powders. Some of asground powders were further subject to ball-milling with charge ratio of 5:1 at a rate of 500 rpm for different milling time, i.e., 0, 4, 8e16 h, where the hardened steel jar and ZrO2 balls were used. The balls and powders in jar were encapsulated under argon protection to avoid oxidation during rapid rotation. The as-milled powders were then annealed at 673 K for 5 h in vacuum quartz tube. The crystal structure analyses were performed with powder Xray diffraction (XRD) using Cu-Ka radiation at room temperature. The actual composition of the homogenized alloy was verified to be Ni50.1Mn25.1Ga24.8 by energy disperse spectroscopy (EDS). The morphology of powder was observed by scanning electron microscope (SEM, JEOL JSM-7001F). The static magnetic measurements were carried out on a vibrating sample magnetometer (VSM, LAKESHORE). The electromagnetic parameters were measured at 2.0e18.0 GHz by using a vector network analyzer (VNA, Keysight N5222A). The powders were uniformly mixed with the paraffin in mass ratio of 2:1 and casted into a toroidal shaped sample with the outer diameter of 7.00 mm and inner diameter of 3.04 mm. 3. Results and discussion 3.1. Crystal structure, morphology and magnetic properties For simplicity, the Ni2MnGa alloy particles with different milling time of 0, 4, 8, and 16 h are denoted as A, B, C and D, respectively.
Table 1 EDS results for samples A-D. Sample
Ni (at. %)
Mn (at. %)
Ga (at. %)
O (at. %)
A B C D
50.1 49.4 49.3 49.1
25.1 24.7 24.5 24.2
24.8 24.3 24.4 24.7
e 1.6 1.8 2.0
Table 1 displays the compositions for the particles determined by EDS. For the sample B, C and D, a slight fraction of O element was introduced, which might be originated from the ethanol that used as lubricant and cooling liquid during ball-milling process. Fig. 1(a) presents the XRD patterns of four samples measured at the room temperature. It is seen that all the samples are in austenite state at the room temperature, with the cubic L21 Heusler structure (space group Fme3m, No. 225). The corresponding lattice parameters are given in Table 1. With increasing the milling time, the intensity of characteristic diffraction peaks gradually decreases and the width increases, as exemplified by the quantitative description on the {220}A diffraction peak (see Table 2). This fact suggests the decreased particle size and the enhanced lattice distortion with increasing the milling time [30]. Besides, the lattice parameter of austenite (a) also gradually decreases as the milling time increases. Fig. 1(b) shows the zoomed patterns in the 2q range of 20 e40 . For sample A, both {111} and {200} peak can be seen. However, for samples B, C and D, the {111} peak is no longer visible and the {200} peak has appeared, suggesting the decrease in the atomic order [31]. For sample D, some other small peaks that do not belong to Heusler structure have appeared, indicating the formation of a new secondary phase induced by the milling of 16 h followed by a heat treatment. This could be due to the minor oxidation of Mn on the surface of particles during the milling process [32]. Fig. 2 shows the morphology and the corresponding size distribution for samples A-D. It is seen that the particles without ballmilling exhibit irregular morphology and asymmetrical particle size, whereas the as-milled particles almost appear to be regular subglobose shape. The average particle size (d) values for all the samples are listed in Table 2. The particle size was measured using the Nano Measurer Software based on SEM images. For each sample, five SEM images were used to ensure the statistical significance. With increasing the milling time from 0 h to 16 h, the d values gradually decrease, i.e., from ~31.0 mm to ~6.9 mm. Keeping the weight unchanged, the increase of particle amounts due to the decrease of particle size may reduce the distance of neighboring particles, resulting in the enhanced space-charge polarization and dielectric loss [33,34]. In addition, the exchange coupling reaction of neighboring particles could also be reinforced due to the decrease of particle size [33,35]. The magnetic hysteresis loops measured at the room temperature for four samples A-D are shown in Fig. 3. All samples exhibit the typical characteristic of soft magnetic materials. The corresponding values of saturation magnetization (Ms), remnant magnetization (Mr), and coercivity (Hc) are summarized in Table 2. The Ms gradually decreases with the increase of the milling time. Such effect could be originated from three aspects. One is the decrease of the particle size [36e38], the other is the destruction of ferromagnetic exchange interaction of MneMn atom pairs caused by severe mechanical deformation in the repeatedly ball-milling process [39,40], and the third is the enhanced atomic disorder due to the introduction of structure defects by ball-milling. Generally, the magnetic moments are localized on Mn atoms and the coupling between adjacent (1/4, 1/4, 1/4) Mn atoms is ferromagnetic. If one (1/4, 1/4, 1/4) Mn atom exchanges its position with one (3/4, 3/4, 3/4) Ga atom, the (3/4, 3/4, 3/4) Mn atom forms antiferromagnetic coupling with neighboring (1/4, 1/4, 1/4) Mn atoms. At the same time, the (1/4, 1/4, 1/4) Ga atom also reduces its own ferromagnetic coupling. These changes reduce the total magnetic moment of the samples. Moreover, Hc is also significantly affected by ball-milling, which may be ascribed to the formation of large amount of defects and the existence of residual strain aroused from the violent deformation during the milling process. These factors would induce higher magnetization resistance on account of pinning effect [41,42].
Please cite this article as: J. Feng et al., Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152588
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Fig. 1. Room temperature powder X-ray diffraction patterns of samples A-D. (a) 2q ¼ 20 e100 . (b) 2q ¼ 20 e40 .
Table 2 Lattice parameters, unit-cell volumes (V), mean particle size (d) and magnetic parameters (Ms, Hc and Mr) for samples A-D. Samples
a¼b¼c
V
Position
A B C D
d
Diffraction peak {220}A FWHM
(Å)
(Å3)
/
5.822 5.821 5.820 5.818
197.34 197.28 197.17 196.93
44.001 44.004 44.035 44.076
0.162 0.227 0.232 0.260
Ms
Mr
Hc
0.3 1.6 1.3 0.7
12.7 84.5 69.8 42.5
Intension
81413 28375 25393 8899
(mm)
(emu/g)
31.0 27.6 11.8 6.9
51.1 43.7 35.3 24.8
(Oe)
Fig. 2. (a)e(d) Microstructure for samples A-D. (e)e(h) Particles size distribution for samples A-D.
3.2. Electromagnetic performance In order to investigate the electromagnetic wave absorption performance, the electromagnetic parameters of the paraffinbonded hybrids containing 66.7 wt% samples A-D (marked as samples SA-SD) were measured at the room temperature in the frequency range of 2e18 GHz. Fig. 4(a) and (b) show the real permittivity (ε0 ) and imagine permittivity (ε00 ) for four samples SASD. For each sample, the values of ε0 are almost constant (i.e., ~5.78, ~4.95, ~3.47 and ~5.46 for samples SA-SD, respectively) before the appearance of the peaks and troughs. On the other hand, the values of ε00 are basically maintained around zero except for the resonant peaks. The peak values of ε00 reach ~3.41 at ~12.0 GHz, ~2.90 at ~13.0 GHz, ~6.81 at ~13.2 GHz, and ~7.00 at ~11.8 GHz for samples SA-SD, respectively. Moreover, it can be found that there exist
frequency intervals in the ε0 and ε00 curves, which represents the resonant characteristics [43]. The corresponding frequency and peak values are summarized in Table 3. It is seen that the resonant peak values increase with the increase of the milling time, suggesting the improved energy consumption ability. It should be stressed that such strong resonance behavior in the range of specific frequency could not be a consequence of a percolation phenomenon [44,45]. The real permeability (m0 ) and imagine permeability (m00 ) for the four samples are shown in Fig. 4(c) and (d). For all the samples, there is a downward trend for both m0 and m00 with increasing the frequency except for an anti-resonance frequency range. It is noted that the locations for the minimum and maximum values of real permeability (m0 ) are just reversal to those of real permittivity (ε0 ), corresponding to the frequency region of 11.4e12.7 GHz (SA),
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Fig. 3. Magnetic hysteresis loops for samples A-D measured at the room temperature. The inset is the corresponding magnifications around the zero magnetic field.
12.4e13.5 GHz (SB), 13.0e13.7 GHz (SC) and 11.6e12.2 GHz (SD). For m00 curve, the values decrease with increasing the milling time. This effect can be ascribed to the reduction of Ms according to the equation of m00 ¼ 1þ(Ms/H)$sinq [46], where H and q represent the intensity of external magnetic field and the phase lag angle of magnetization behind external magnetic field, respectively. It should be stressed that compared to the sample without ballmilling, the reinforced negative peaks at the frequency of ~13.1 GHz (SB), ~13.3 GHz (SC) and ~11.9 GHz (SD) can be observed for all the milled samples. Meanwhile, an enhanced resource peak
of the ε00 at the same frequency range emerges. Interestingly, the values of the enhanced ε00 and weakened m00 strongly depend on the ball-milling time and they exhibit a positive correlation. This phenomenon is quite similar to the feature of resonant-antiresonant behavior in some metamaterials [47,48] and nanocomposites [28,29,49]. Zhang et al. [28] pointed out that this antiresonantresonant behavior may occur when the distance between neighboring close-packed Ni nanoparticles was smaller than a critical distance. Wang et al. [50] stated that this phenomenon may be related to the multi-loss combination, such as the dipole polarizations, interfacial polarization and conductance loss, due to the unique structure of a-Fe2O3/OMC. In this work, we believe that the enhanced dielectric resonance and weakened magnetic antiresonance are related to the increase of dipolar polarization associated with defects and residual stress caused by high-energy ballmilling. Another reason could be the near-field electromagnetic interaction induced by the reduced distance of neighboring particles with the decrease of particle size in samples SB-SD. It is noted that the appearance of negative m00 values for samples SB-SD may indicate that the magnetic energy of EMW is radiated and/ or transferred. The magnetic behavior and dielectric behavior can be coupled between natural magnetic resonance and dielectric polarization [51e53]. The enhanced dielectric resonance and weakened magnetic anti-resonance are relevant with the permeability to permittivity transformation in the propagation process, but the total EMW energy has no change. In order to evaluate the EMW energy loss in medium, the effective refractive index nr¼(εrmr)1/2, which is proportional to the electromagnetic attenuation, is calculated. The real part, imaginary part, and modulus of nr for all samples SA-SD are shown in Fig. 5. It is seen that no singularity appears at resonant frequency of ~12.1 GHz (SA), ~13.1 GHz (SB), ~13.3 GHz (SC) and ~11.9 GHz (SD), which confirms that the additional dielectric loss is related to the anti-resonance behavior of permeability [28].
Fig. 4. Electromagnetic response properties for sample SA-SD: (a) real and (b) imaginary parts of the relative complex permittivity, (c) real and (d) imaginary parts of the relative complex permeability.
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Table 3 Detailed complex dielectric value and occurring frequency of the peaks and troughs for samples SA-SD. Samples
value and occurring frequency Peak
Trough
0
ε’
ε SA SB SC SD
6.64 at 6.59 at 7.03 at 8.90 at
11.3 GHz 12.3 GHz 12.9 GHz 11.6 GHz
m
0
3.41 at 2.90 at 6.18 at 7.00 at
12.0 GHz 13.0 GHz 13.2 GHz 11.8 GHz
m’0
0
0.85 at 0.96 at 1.23 at 1.30 at
12.7 GHz 13.5 GHz 13.5 GHz 12.2 GHz
0.07 at 12.1 GHz 0.05 at 13.1 GHz 0.31 at 13.3 GHz 0.34 at 11.9 GHz
3.3. Microwave absorbing performance To further compare and evaluate the EMW absorption properties for the studied samples, the reflection loss (RL, dB) is quantitatively calculated with the following equations [54]:
Z Z 0 RL ¼ 20lg in Zin Z0
Zin ¼ Z0
rffiffiffiffiffi mr 2pfd pffiffiffiffiffiffiffiffiffi tanh j mr εr c εr
(1)
(2)
where Zin, Z0, f, d and c represent the normalized input impedance of the absorber, the impedance of free space, the frequency of EMW, the thickness of the absorber and the velocity of light, respectively. Generally, the RL values of 10 dB and 20 dB correspond to the EMW energy of 90% and 99% that can be efficiently absorbed. The frequency dependent RL values at the thickness of 2.40 mm for all the samples are shown in Fig. 6. For the sample without ballmilling, there is one peak at ~13.1 GHz with a minimum RL (RLmin) of 21.3 dB. For the samples subject to ball-milling, there are strong continuous dual-absorption peaks (denoted as P1 and P2 in the figure), where the corresponding peak RL values are 10.5 dB at ~12.5 GHz and 25.3 dB at ~16.0 GHz for sample SB, 21.4 dB at ~12.9 GHz and 25.9 dB at ~16.9 GHz for sample SC, and 30.9 dB at ~11.6 GHz and 39.0 dB at ~14.5 GHz for sample SD, respectively. Among the four samples, sample SD shows the optimal EMW absorption with the RLmin value of 39.0 dB at ~14.5 GHz. Accordingly, owing to the dual-absorption peaks, the absorption bandwidth with RL 10 dB increases from 3.2 GHz (sample SA) to 5.3 GHz (sample SD). These results indicate that the
Fig. 5. The real part, imaginary part and modulus of nr for samples SA-SD at 2.0e18.0 GHz.
Fig. 6. Comparison of reflection loss values at 2.40 mm for samples SA-SD.
ball-milling has resulted in the considerable enhancement on the electromagnetic performance. It is noted that the present continuous dual-absorption phenomenon is realized in micron-sized ferromagnetic particles prepared by simple ball-milling, rather than the nanostructured composites [5e7,55,56]. It is known that the thickness of the absorber has a significant influence on RL values and the frequency of maximum absorption. Hence, the three-dimensional RL mapping at the thickness range from 0.1 mm to 5.0 mm with an interval of 0.01 mm for all samples SA-SD are shown in Fig. 7(a)-(d). For the sample without ballmilling (sample SA), the RLmin value is 49.1 dB at 13.3 GHz with the thickness of 2.57 mm, and the effective absorption bandwidth with RL values less than 10 dB is 11.7 GHz (6.3e18.0 GHz) by altering the thickness from 1.66 to 4.76 mm. It is worth noting that the samples after ball-milling present more remarkable absorption abilities. For example, the RLmin value of sample SD is improved to 65.2 dB at a frequency of 14.4 GHz with the thickness of 2.90 mm, and the effective absorption bandwidth (RL values below 10 dB) can reach 12.7 GHz (5.3e18.0 GHz) through varying the thickness of 1.65e5.00 mm. Such enhancement of EMW absorbing properties could be originated from the anomalously electromagnetic resonance associated with the transformation between the permeability and permittivity and the optimal impedance matching character. Table 4 compares the EMW absorbing performance of the present samples with some representative EMW absorbing materials in the literatures. It is evident that the EMW absorbing properties of as-milled Ni2MnGa particles are indeed superior to some other materials. Fig. 7(e)e(h) shows the calculated RL plots with the given thickness for all samples SA-SD. The distinct dual-absorption peaks
Please cite this article as: J. Feng et al., Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152588
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Fig. 7. EMW absorbing performance for samples SA-SD. (a)e(d) Three-dimensional (3D) plots of RL, frequency and thickness. (e)e(h) Frequency dependence of RL curves for sim representative thickness corresponding to above 3D mapping. (i)e(l) Variation of calculated (dcal m ) and simulated (dm ) thickness as a function of frequency according to quarterwavelength model.
Table 4 Comparison on the microwave absorption properties between the present work and those in literatures. Samples
Particle size
RLmin
mm
dB
GHz
mm
RL 20
RL 10
RL 20
RL 10
SA SB SC SD Fe3O4@C Fe@ZnO Fe3O4/C AgFe/Fe3O4 Fe3O4/Fe@C NRs
~31.0 ~27.6 ~11.8 ~6.9 0.5 1e2.5 102 1.4 102 6.5e9.0 102 0.8e3.0
49.1 56.3 47.8 65.2 20.0 57.1 46.0 49.7 28.2
13.3 12.5 12.9 14.4 12.1 7.8 12.8 10.88 4.94
2.57 2.28 2.69 2.90 e 3.00 2.9 2.0 2.0
10.3e14.6, 15.0e15.9 11.5e12.9, 14.4e18.0 11.7e13.0, 16.2e18.0 9.0e11.7, 13.0e17.7 12.0e14.0 6.1e15.7 7.0e16.8 8.4e13.7, 16.2e18.0 3.2e9.5, 16.2e16.6
6.3e18.0 7.4e18.0 7.5e18.0 5.3e18.0 9.0e15.7 e 10.3e17.1 e e
1.91e3.08 2.01e2.98 2.12e3.03 1.88e3.40 2.0e2.5 1.5e5.0 2.5e4.5 1.85e5.3 3.0e7.0
1.66e4.76 1.82e4.62 1.90e4.69 1.65e5.00 2.3e2.7 e 1.5e2.2 e e
fm
dm
Bandwidth (GHz)
can be observed for samples SB-SD but only mono-absorption peak for sample SA. The generation of these peaks could be ascribed to the resonant absorption caused by the quarter-wavelength (nl/4) mechanism (known as “geometrical effect”) [62,63]. It is obvious that the observed RL peaks shift towards lower frequency region with increasing thickness, which can be interpreted by the following formula:
dm ¼
4fm
nc pffiffiffiffiffiffiffiffiffiffiffiffi jεr mr j
(3)
where n is a positive odd 1, 3, 5 …, dm and fm denote the matching thickness and the peak frequency.
Thickness (mm)
Refs.
This work
[57] [58] [59] [60] [61]
cal The simulated (dsim m ) and calculated (dm ) thickness evaluated by Equations (2) and (3) for samples SA-SD at the same l/4 curves (n ¼ 1) are shown in Fig. 7(i)e(l). The observed minimum RL peaks in Fig. 7(e)e(h) corresponding to the given thickness (dsim m ) of Fig. 7(i)e(l) are linked with the vertical dash lines. It is seen that the l/4 curves of calculated thickness (dcal m ) at various thickness are nearly or exactly in agreement with the simulated thickness (dsim m ) marked by solid dot except for sample SA. It implies that the incident and reflected wave could create standing wave at the airabsorber interface and thus enhanced the EMW loss [64]. Furthermore, the RL peaks appear at the given thickness of 2.30, 2.70 and 2.90 mm (marked by the violet dash line) which are close
Please cite this article as: J. Feng et al., Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152588
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to the optimal thickness (dm) in Table 4, in which the dsim m is consistent with the dcal m . Thus, the geometrical effect at proper thickness could also result in the enhancement of the EMW absorbing properties. As expected, sample SD exhibits the most remarkable EMW absorption performance among the studied samples. 4. Conclusions In summary, the magnetic and EMW absorbing properties of Ni2MnGa microparticles prepared by ball-milling have been systematically investigated. It is found that the samples after ballmilling present enhanced dielectric loss and weakened magnetic loss (resonance-antiresonance behavior) associated with the permeability-to-permittivity transformation at a specific frequency region. All the milled samples exhibit prominently continuous dual-absorption peaks, which substantially broaden the effective absorption bandwidth. The samples with milling time of 16 h exhibit optimal EMW absorbing performance, where the RLmin value of 65.2 dB is achieved at 14.4 GHz with a thickness of 2.90 mm. The present work further extends the domain of functional behavior for Heusler-type NiMn-based alloys. It is demonstrated that Heusler type NiMn-based alloys could be a competitive candidate for EMW absorption applications. Acknowledgment This work was supported by the National Natural Science Foundation of China (Grant Nos. 51571056, 51771048), the Fundamental Research Funds for the Central Universities of China (Grant Nos. N180204013, N170908001 and N170904001), the Liaoning Revitalization Talents Program (Grant No. XLYC1802023) and the Research Funds for Innovation Talents in Universities and Colleges of Liaoning Province (Grant No. LR2016003). References [1] X.F. Liu, Y.X. Chen, X.R. Cui, M. Zeng, R.H. Yu, G.S. Wang, J. Mater. Chem. 3 (2015) 12197e12204. [2] P.Y. Liu, L.M. Wang, B. Cao, L.C. Li, K.L. Zhang, X.M. Bian, Z.L. Hou, J. Mater. Chem. C 5 (2017) 6745e6754. [3] N. Zhang, Y. Huang, M. Zong, X. Ding, S.P. Li, M.Y. Wang, Chem. Eng. J. 308 (2017) 214e221. [4] H.F. Li, J. Wang, Y.H. Huang, X.Q. Yan, J.J. Qi, J. Liu, Y. Zhang, Mater. Sci. Eng. B 175 (2010) 81e85. [5] D.P. Sun, Q. Zou, G.Q. Qian, C. Sun, W. Jiang, F.S. Li, Acta Mater. 61 (2013) 5829e5834. [6] T.T. Chen, F. Deng, J. Zhu, C.F. Chen, G.B. Sun, S.L. Ma, X.J. Yang, J. Mater. Chem. 22 (2012) 15190e15197. [7] X.F. Liu, X.Y. Nie, R.H. Yu, H.B. Feng, Chem. Eng. J. 334 (2018) 153e161. [8] X. Wang, R.Z. Gong, P.G. Li, L.Y. Liu, W.M. Cheng, Mater. Sci. Eng. A 466 (2007) 178e182. vet-Vincent, F. Fie vet, Adv. Mater. 10 [9] P. Toneguzzo, G. Viau, O. Acher, F. Fie (1998) 1032e1035. [10] V.F. Meshcheryakov, Y.K. Fetisov, A.A. Stashkevich, G. Viau, J. Appl. Phys. 104 (2008), 063910. [11] C. Liu, Y. Yuan, J.T. Jiang, Y.X. Gong, L. Zhen, J. Magn. Magn. Mater. 395 (2015) 152e158. [12] S.J. Yan, L. Zhen, C.Y. Xu, J.T. Jiang, W.Z. Shao, J.K. Tang, J. Magn. Magn. Mater. 323 (2011) 515e520. [13] Q.R. Jiang, H.L. Li, Z.M. Cao, H. Li, Q.X. Wang, Z.Y. Jiang, Q. Kuang, Z.X. Xie, J. Alloy. Comp. 726 (2017) 1255e1261. [14] Z.X. Yu, N. Zhang, Z.P. Yao, X.J. Han, Z.H. Jiang, J. Mater. Chem. 1 (2013) 12462e12470. [15] L.N. Huang, X.F. Liu, D. Chuai, Y.X. Chen, R.H. Yu, Sci. Rep. 6 (2016) 35377. [16] S. Pandey, S. Vyzulin, A. Quetz, A. Aryal, I. Dubenko, A. Granovsky, S. Stadler, N. Ali, AIP Adv. 8 (2018), 056707. [17] J. Feng, Z.B. Li, Y.S. Jia, B. Yang, S.J. Liu, X. Zhao, L.W. Li, L. Zuo, J. Mater. Sci. 53 (2018) 11779e17790. [18] K. Ullakko, J.K. Huang, C. Kantner, R.C. O’Handley, V.V. Kokorin, Appl. Phys.
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks Jing Feng a, b, Zongbin Li a, *, Dong Li a, Bo Yang a, Lingwei Li c, **, Xiang Zhao a, Liang Zuo a a
Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang, 110819, PR China b State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200030, PR China c Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang, 110819, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 June 2019 Received in revised form 7 September 2019 Accepted 5 October 2019 Available online xxx
Achieving continuous dual-absorption peaks in ferromagnetic materials with micron-sized particles is quite challenging in designing the potential electromagnetic wave (EMW) absorbing materials. Here, we realize this effect in ball-milled Ni2MnGa microparticles and report their EMW absorbing properties for the first time. The as-milled Ni2MnGa/paraffin-bonded hybrids exhibit highly efficient EMW absorbing performance owing to the continuous dual-absorption peaks induced by enhanced dielectric loss and weakened magnetic loss associated with the permeability-to-permittivity energy transformation at the frequency of 2.0e18.0 GHz. The optimal EMW absorbing properties with the RLmin value up to 65.2 dB can be obtained at a frequency of ~14.4 GHz with a thickness of 2.90 mm. The effective absorption bandwidth with RL values less than 10 dB can reach 12.7 GHz through tuning the absorber thickness. It is demonstrated that Heusler-type NiMn-based alloys could be an attractive mono-component ferromagnetic absorber with highly efficient dual-absorption peaks. © 2019 Elsevier B.V. All rights reserved.
Keywords: Ni2MnGa Heusler alloy Electromagnetic absorption Dual-absorption peaks Ball milling
1. Introduction The wide applications of wireless communications and highfrequency electronic devices have given rise to significant electromagnetic wave pollution in our surroundings. To eliminate such detrimental effect, high-performance electromagnetic absorption materials (EMAMs), with the combination of broad bandwidth, light weight, thin thickness and good thermal and chemical stability, are highly desired [1e4]. In fact, the excellent electromagnetic absorbing performance of any EMAMs could mainly be achieved through improving the impedance matching associated with their intrinsic electromagnetic parameters of the complex permeability and permittivity (m0 , m00 , ε0 , ε00 ). Along this line, considerable efforts have been devoted to designing and fabricating diverse absorbers, e.g., magnetic, dielectric and magnetic-dielectric composites, to realize optimal electromagnetic wave (EMW) absorption. In recent years, some magnetic-dielectric nanocomposites such as Fe3O4/graphene [5], Ni/graphene [6], CuS/Ag2S
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (Z. Li), [email protected] (L. Li).
[7], are found to exhibit enhanced EMW absorbing properties, since the dual-absorption peaks enable broader bandwidth with respect to that of mono-component absorbent. Although the bonus of dualabsorption peaks in magnetic-dielectric nanocomposites has been well acknowledged, the complicated preparation processes and poor thermal and environmental stability impose strong constraints on their practical applications. Recently, it has been found that some ferromagnetic materials exhibit good EMW absorption properties at relatively high frequency, with the advantages in matching the electromagnetic parameters (m0 , m00 , ε0 , ε00 ) through tuning the composition, microstructure, particle size and morphology [8e15]. Especially, ferromagnetic Heusler-type NiMn-based alloys have attracted considerable attention in last twenty years, not only because of their unusual resonance behaviors [16,17], but also due to their multifunctional features, such as magnetic shape memory effect (MSME) [18e20], magnetocaloric effect (MCE) [21e24], magnetoresistance effect (MRE) [25], and elastocaloric effect [26,27]. Besides, our recent results show that the ferromagnetic Ni2þxMn1-xGa alloy particles also possess significant high-frequency EMW absorption performance [17], which enlarges the frontier of functional behaviors for these alloys. Unfortunately, the narrow effective
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Please cite this article as: J. Feng et al., Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152588
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absorption bandwidth still represents a substantial drawback in view of the potential applications. In this regard, exploring dualabsorption peaks is a feasible strategy to extend the bandwidth. Although the dual-absorption peaks have been experimentally observed in the shell@core nanocomposites [28,29], the realization of dual-absorption peaks in ferromagnetic particles, especially the newly developed NiMn-based alloys, is still a primary challenge. In this work, we report the enhanced EMW absorbing performance due to the continuous dual-absorption peaks in Ni2MnGa microparticles prepared by ball-milling. It is shown that the microparticles with milling time of 16 h exhibits the optimal EMW absorbing performance, where the RLmin value of 65.2 dB is achieved at ~14.4 GHz with a thickness of 2.90 mm. Moreover, the effective absorption bandwidth with RL value less than 10 dB can reach ~12.7 GHz with a thickness range of 1.65e5.00 mm, due to the continuous dual-absorption peaks induced by enhanced dielectric resonance and weakened magnetic anti-resonance. The present work is the first report on the continuous dual-absorption peaks in NiMn-based alloy microparticles. It is demonstrated that the mechanical ball-milling is an efficient processing route to tune the EMW absorption performance for the NiMn-based alloys. 2. Experimental Stoichiometric Ni2MnGa polycrystalline alloy was prepared by arc-melting in argon atmosphere with high-purity raw elements nickel (4 N), manganese (3 N), and gallium (4 N). In order to achieve a good composition homogenization, the as-cast ingot was then encapsulated in a vacuum quartz tube and annealed at 1173 K for 36 h, followed by quenching into water. The homogenized ingot was mechanically crushed and ground into powders. Some of asground powders were further subject to ball-milling with charge ratio of 5:1 at a rate of 500 rpm for different milling time, i.e., 0, 4, 8e16 h, where the hardened steel jar and ZrO2 balls were used. The balls and powders in jar were encapsulated under argon protection to avoid oxidation during rapid rotation. The as-milled powders were then annealed at 673 K for 5 h in vacuum quartz tube. The crystal structure analyses were performed with powder Xray diffraction (XRD) using Cu-Ka radiation at room temperature. The actual composition of the homogenized alloy was verified to be Ni50.1Mn25.1Ga24.8 by energy disperse spectroscopy (EDS). The morphology of powder was observed by scanning electron microscope (SEM, JEOL JSM-7001F). The static magnetic measurements were carried out on a vibrating sample magnetometer (VSM, LAKESHORE). The electromagnetic parameters were measured at 2.0e18.0 GHz by using a vector network analyzer (VNA, Keysight N5222A). The powders were uniformly mixed with the paraffin in mass ratio of 2:1 and casted into a toroidal shaped sample with the outer diameter of 7.00 mm and inner diameter of 3.04 mm. 3. Results and discussion 3.1. Crystal structure, morphology and magnetic properties For simplicity, the Ni2MnGa alloy particles with different milling time of 0, 4, 8, and 16 h are denoted as A, B, C and D, respectively.
Table 1 EDS results for samples A-D. Sample
Ni (at. %)
Mn (at. %)
Ga (at. %)
O (at. %)
A B C D
50.1 49.4 49.3 49.1
25.1 24.7 24.5 24.2
24.8 24.3 24.4 24.7
e 1.6 1.8 2.0
Table 1 displays the compositions for the particles determined by EDS. For the sample B, C and D, a slight fraction of O element was introduced, which might be originated from the ethanol that used as lubricant and cooling liquid during ball-milling process. Fig. 1(a) presents the XRD patterns of four samples measured at the room temperature. It is seen that all the samples are in austenite state at the room temperature, with the cubic L21 Heusler structure (space group Fme3m, No. 225). The corresponding lattice parameters are given in Table 1. With increasing the milling time, the intensity of characteristic diffraction peaks gradually decreases and the width increases, as exemplified by the quantitative description on the {220}A diffraction peak (see Table 2). This fact suggests the decreased particle size and the enhanced lattice distortion with increasing the milling time [30]. Besides, the lattice parameter of austenite (a) also gradually decreases as the milling time increases. Fig. 1(b) shows the zoomed patterns in the 2q range of 20 e40 . For sample A, both {111} and {200} peak can be seen. However, for samples B, C and D, the {111} peak is no longer visible and the {200} peak has appeared, suggesting the decrease in the atomic order [31]. For sample D, some other small peaks that do not belong to Heusler structure have appeared, indicating the formation of a new secondary phase induced by the milling of 16 h followed by a heat treatment. This could be due to the minor oxidation of Mn on the surface of particles during the milling process [32]. Fig. 2 shows the morphology and the corresponding size distribution for samples A-D. It is seen that the particles without ballmilling exhibit irregular morphology and asymmetrical particle size, whereas the as-milled particles almost appear to be regular subglobose shape. The average particle size (d) values for all the samples are listed in Table 2. The particle size was measured using the Nano Measurer Software based on SEM images. For each sample, five SEM images were used to ensure the statistical significance. With increasing the milling time from 0 h to 16 h, the d values gradually decrease, i.e., from ~31.0 mm to ~6.9 mm. Keeping the weight unchanged, the increase of particle amounts due to the decrease of particle size may reduce the distance of neighboring particles, resulting in the enhanced space-charge polarization and dielectric loss [33,34]. In addition, the exchange coupling reaction of neighboring particles could also be reinforced due to the decrease of particle size [33,35]. The magnetic hysteresis loops measured at the room temperature for four samples A-D are shown in Fig. 3. All samples exhibit the typical characteristic of soft magnetic materials. The corresponding values of saturation magnetization (Ms), remnant magnetization (Mr), and coercivity (Hc) are summarized in Table 2. The Ms gradually decreases with the increase of the milling time. Such effect could be originated from three aspects. One is the decrease of the particle size [36e38], the other is the destruction of ferromagnetic exchange interaction of MneMn atom pairs caused by severe mechanical deformation in the repeatedly ball-milling process [39,40], and the third is the enhanced atomic disorder due to the introduction of structure defects by ball-milling. Generally, the magnetic moments are localized on Mn atoms and the coupling between adjacent (1/4, 1/4, 1/4) Mn atoms is ferromagnetic. If one (1/4, 1/4, 1/4) Mn atom exchanges its position with one (3/4, 3/4, 3/4) Ga atom, the (3/4, 3/4, 3/4) Mn atom forms antiferromagnetic coupling with neighboring (1/4, 1/4, 1/4) Mn atoms. At the same time, the (1/4, 1/4, 1/4) Ga atom also reduces its own ferromagnetic coupling. These changes reduce the total magnetic moment of the samples. Moreover, Hc is also significantly affected by ball-milling, which may be ascribed to the formation of large amount of defects and the existence of residual strain aroused from the violent deformation during the milling process. These factors would induce higher magnetization resistance on account of pinning effect [41,42].
Please cite this article as: J. Feng et al., Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152588
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Fig. 1. Room temperature powder X-ray diffraction patterns of samples A-D. (a) 2q ¼ 20 e100 . (b) 2q ¼ 20 e40 .
Table 2 Lattice parameters, unit-cell volumes (V), mean particle size (d) and magnetic parameters (Ms, Hc and Mr) for samples A-D. Samples
a¼b¼c
V
Position
A B C D
d
Diffraction peak {220}A FWHM
(Å)
(Å3)
/
5.822 5.821 5.820 5.818
197.34 197.28 197.17 196.93
44.001 44.004 44.035 44.076
0.162 0.227 0.232 0.260
Ms
Mr
Hc
0.3 1.6 1.3 0.7
12.7 84.5 69.8 42.5
Intension
81413 28375 25393 8899
(mm)
(emu/g)
31.0 27.6 11.8 6.9
51.1 43.7 35.3 24.8
(Oe)
Fig. 2. (a)e(d) Microstructure for samples A-D. (e)e(h) Particles size distribution for samples A-D.
3.2. Electromagnetic performance In order to investigate the electromagnetic wave absorption performance, the electromagnetic parameters of the paraffinbonded hybrids containing 66.7 wt% samples A-D (marked as samples SA-SD) were measured at the room temperature in the frequency range of 2e18 GHz. Fig. 4(a) and (b) show the real permittivity (ε0 ) and imagine permittivity (ε00 ) for four samples SASD. For each sample, the values of ε0 are almost constant (i.e., ~5.78, ~4.95, ~3.47 and ~5.46 for samples SA-SD, respectively) before the appearance of the peaks and troughs. On the other hand, the values of ε00 are basically maintained around zero except for the resonant peaks. The peak values of ε00 reach ~3.41 at ~12.0 GHz, ~2.90 at ~13.0 GHz, ~6.81 at ~13.2 GHz, and ~7.00 at ~11.8 GHz for samples SA-SD, respectively. Moreover, it can be found that there exist
frequency intervals in the ε0 and ε00 curves, which represents the resonant characteristics [43]. The corresponding frequency and peak values are summarized in Table 3. It is seen that the resonant peak values increase with the increase of the milling time, suggesting the improved energy consumption ability. It should be stressed that such strong resonance behavior in the range of specific frequency could not be a consequence of a percolation phenomenon [44,45]. The real permeability (m0 ) and imagine permeability (m00 ) for the four samples are shown in Fig. 4(c) and (d). For all the samples, there is a downward trend for both m0 and m00 with increasing the frequency except for an anti-resonance frequency range. It is noted that the locations for the minimum and maximum values of real permeability (m0 ) are just reversal to those of real permittivity (ε0 ), corresponding to the frequency region of 11.4e12.7 GHz (SA),
Please cite this article as: J. Feng et al., Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152588
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Fig. 3. Magnetic hysteresis loops for samples A-D measured at the room temperature. The inset is the corresponding magnifications around the zero magnetic field.
12.4e13.5 GHz (SB), 13.0e13.7 GHz (SC) and 11.6e12.2 GHz (SD). For m00 curve, the values decrease with increasing the milling time. This effect can be ascribed to the reduction of Ms according to the equation of m00 ¼ 1þ(Ms/H)$sinq [46], where H and q represent the intensity of external magnetic field and the phase lag angle of magnetization behind external magnetic field, respectively. It should be stressed that compared to the sample without ballmilling, the reinforced negative peaks at the frequency of ~13.1 GHz (SB), ~13.3 GHz (SC) and ~11.9 GHz (SD) can be observed for all the milled samples. Meanwhile, an enhanced resource peak
of the ε00 at the same frequency range emerges. Interestingly, the values of the enhanced ε00 and weakened m00 strongly depend on the ball-milling time and they exhibit a positive correlation. This phenomenon is quite similar to the feature of resonant-antiresonant behavior in some metamaterials [47,48] and nanocomposites [28,29,49]. Zhang et al. [28] pointed out that this antiresonantresonant behavior may occur when the distance between neighboring close-packed Ni nanoparticles was smaller than a critical distance. Wang et al. [50] stated that this phenomenon may be related to the multi-loss combination, such as the dipole polarizations, interfacial polarization and conductance loss, due to the unique structure of a-Fe2O3/OMC. In this work, we believe that the enhanced dielectric resonance and weakened magnetic antiresonance are related to the increase of dipolar polarization associated with defects and residual stress caused by high-energy ballmilling. Another reason could be the near-field electromagnetic interaction induced by the reduced distance of neighboring particles with the decrease of particle size in samples SB-SD. It is noted that the appearance of negative m00 values for samples SB-SD may indicate that the magnetic energy of EMW is radiated and/ or transferred. The magnetic behavior and dielectric behavior can be coupled between natural magnetic resonance and dielectric polarization [51e53]. The enhanced dielectric resonance and weakened magnetic anti-resonance are relevant with the permeability to permittivity transformation in the propagation process, but the total EMW energy has no change. In order to evaluate the EMW energy loss in medium, the effective refractive index nr¼(εrmr)1/2, which is proportional to the electromagnetic attenuation, is calculated. The real part, imaginary part, and modulus of nr for all samples SA-SD are shown in Fig. 5. It is seen that no singularity appears at resonant frequency of ~12.1 GHz (SA), ~13.1 GHz (SB), ~13.3 GHz (SC) and ~11.9 GHz (SD), which confirms that the additional dielectric loss is related to the anti-resonance behavior of permeability [28].
Fig. 4. Electromagnetic response properties for sample SA-SD: (a) real and (b) imaginary parts of the relative complex permittivity, (c) real and (d) imaginary parts of the relative complex permeability.
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Table 3 Detailed complex dielectric value and occurring frequency of the peaks and troughs for samples SA-SD. Samples
value and occurring frequency Peak
Trough
0
ε’
ε SA SB SC SD
6.64 at 6.59 at 7.03 at 8.90 at
11.3 GHz 12.3 GHz 12.9 GHz 11.6 GHz
m
0
3.41 at 2.90 at 6.18 at 7.00 at
12.0 GHz 13.0 GHz 13.2 GHz 11.8 GHz
m’0
0
0.85 at 0.96 at 1.23 at 1.30 at
12.7 GHz 13.5 GHz 13.5 GHz 12.2 GHz
0.07 at 12.1 GHz 0.05 at 13.1 GHz 0.31 at 13.3 GHz 0.34 at 11.9 GHz
3.3. Microwave absorbing performance To further compare and evaluate the EMW absorption properties for the studied samples, the reflection loss (RL, dB) is quantitatively calculated with the following equations [54]:
Z Z 0 RL ¼ 20lg in Zin Z0
Zin ¼ Z0
rffiffiffiffiffi mr 2pfd pffiffiffiffiffiffiffiffiffi tanh j mr εr c εr
(1)
(2)
where Zin, Z0, f, d and c represent the normalized input impedance of the absorber, the impedance of free space, the frequency of EMW, the thickness of the absorber and the velocity of light, respectively. Generally, the RL values of 10 dB and 20 dB correspond to the EMW energy of 90% and 99% that can be efficiently absorbed. The frequency dependent RL values at the thickness of 2.40 mm for all the samples are shown in Fig. 6. For the sample without ballmilling, there is one peak at ~13.1 GHz with a minimum RL (RLmin) of 21.3 dB. For the samples subject to ball-milling, there are strong continuous dual-absorption peaks (denoted as P1 and P2 in the figure), where the corresponding peak RL values are 10.5 dB at ~12.5 GHz and 25.3 dB at ~16.0 GHz for sample SB, 21.4 dB at ~12.9 GHz and 25.9 dB at ~16.9 GHz for sample SC, and 30.9 dB at ~11.6 GHz and 39.0 dB at ~14.5 GHz for sample SD, respectively. Among the four samples, sample SD shows the optimal EMW absorption with the RLmin value of 39.0 dB at ~14.5 GHz. Accordingly, owing to the dual-absorption peaks, the absorption bandwidth with RL 10 dB increases from 3.2 GHz (sample SA) to 5.3 GHz (sample SD). These results indicate that the
Fig. 5. The real part, imaginary part and modulus of nr for samples SA-SD at 2.0e18.0 GHz.
Fig. 6. Comparison of reflection loss values at 2.40 mm for samples SA-SD.
ball-milling has resulted in the considerable enhancement on the electromagnetic performance. It is noted that the present continuous dual-absorption phenomenon is realized in micron-sized ferromagnetic particles prepared by simple ball-milling, rather than the nanostructured composites [5e7,55,56]. It is known that the thickness of the absorber has a significant influence on RL values and the frequency of maximum absorption. Hence, the three-dimensional RL mapping at the thickness range from 0.1 mm to 5.0 mm with an interval of 0.01 mm for all samples SA-SD are shown in Fig. 7(a)-(d). For the sample without ballmilling (sample SA), the RLmin value is 49.1 dB at 13.3 GHz with the thickness of 2.57 mm, and the effective absorption bandwidth with RL values less than 10 dB is 11.7 GHz (6.3e18.0 GHz) by altering the thickness from 1.66 to 4.76 mm. It is worth noting that the samples after ball-milling present more remarkable absorption abilities. For example, the RLmin value of sample SD is improved to 65.2 dB at a frequency of 14.4 GHz with the thickness of 2.90 mm, and the effective absorption bandwidth (RL values below 10 dB) can reach 12.7 GHz (5.3e18.0 GHz) through varying the thickness of 1.65e5.00 mm. Such enhancement of EMW absorbing properties could be originated from the anomalously electromagnetic resonance associated with the transformation between the permeability and permittivity and the optimal impedance matching character. Table 4 compares the EMW absorbing performance of the present samples with some representative EMW absorbing materials in the literatures. It is evident that the EMW absorbing properties of as-milled Ni2MnGa particles are indeed superior to some other materials. Fig. 7(e)e(h) shows the calculated RL plots with the given thickness for all samples SA-SD. The distinct dual-absorption peaks
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J. Feng et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Fig. 7. EMW absorbing performance for samples SA-SD. (a)e(d) Three-dimensional (3D) plots of RL, frequency and thickness. (e)e(h) Frequency dependence of RL curves for sim representative thickness corresponding to above 3D mapping. (i)e(l) Variation of calculated (dcal m ) and simulated (dm ) thickness as a function of frequency according to quarterwavelength model.
Table 4 Comparison on the microwave absorption properties between the present work and those in literatures. Samples
Particle size
RLmin
mm
dB
GHz
mm
RL 20
RL 10
RL 20
RL 10
SA SB SC SD Fe3O4@C Fe@ZnO Fe3O4/C AgFe/Fe3O4 Fe3O4/Fe@C NRs
~31.0 ~27.6 ~11.8 ~6.9 0.5 1e2.5 102 1.4 102 6.5e9.0 102 0.8e3.0
49.1 56.3 47.8 65.2 20.0 57.1 46.0 49.7 28.2
13.3 12.5 12.9 14.4 12.1 7.8 12.8 10.88 4.94
2.57 2.28 2.69 2.90 e 3.00 2.9 2.0 2.0
10.3e14.6, 15.0e15.9 11.5e12.9, 14.4e18.0 11.7e13.0, 16.2e18.0 9.0e11.7, 13.0e17.7 12.0e14.0 6.1e15.7 7.0e16.8 8.4e13.7, 16.2e18.0 3.2e9.5, 16.2e16.6
6.3e18.0 7.4e18.0 7.5e18.0 5.3e18.0 9.0e15.7 e 10.3e17.1 e e
1.91e3.08 2.01e2.98 2.12e3.03 1.88e3.40 2.0e2.5 1.5e5.0 2.5e4.5 1.85e5.3 3.0e7.0
1.66e4.76 1.82e4.62 1.90e4.69 1.65e5.00 2.3e2.7 e 1.5e2.2 e e
fm
dm
Bandwidth (GHz)
can be observed for samples SB-SD but only mono-absorption peak for sample SA. The generation of these peaks could be ascribed to the resonant absorption caused by the quarter-wavelength (nl/4) mechanism (known as “geometrical effect”) [62,63]. It is obvious that the observed RL peaks shift towards lower frequency region with increasing thickness, which can be interpreted by the following formula:
dm ¼
4fm
nc pffiffiffiffiffiffiffiffiffiffiffiffi jεr mr j
(3)
where n is a positive odd 1, 3, 5 …, dm and fm denote the matching thickness and the peak frequency.
Thickness (mm)
Refs.
This work
[57] [58] [59] [60] [61]
cal The simulated (dsim m ) and calculated (dm ) thickness evaluated by Equations (2) and (3) for samples SA-SD at the same l/4 curves (n ¼ 1) are shown in Fig. 7(i)e(l). The observed minimum RL peaks in Fig. 7(e)e(h) corresponding to the given thickness (dsim m ) of Fig. 7(i)e(l) are linked with the vertical dash lines. It is seen that the l/4 curves of calculated thickness (dcal m ) at various thickness are nearly or exactly in agreement with the simulated thickness (dsim m ) marked by solid dot except for sample SA. It implies that the incident and reflected wave could create standing wave at the airabsorber interface and thus enhanced the EMW loss [64]. Furthermore, the RL peaks appear at the given thickness of 2.30, 2.70 and 2.90 mm (marked by the violet dash line) which are close
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to the optimal thickness (dm) in Table 4, in which the dsim m is consistent with the dcal m . Thus, the geometrical effect at proper thickness could also result in the enhancement of the EMW absorbing properties. As expected, sample SD exhibits the most remarkable EMW absorption performance among the studied samples. 4. Conclusions In summary, the magnetic and EMW absorbing properties of Ni2MnGa microparticles prepared by ball-milling have been systematically investigated. It is found that the samples after ballmilling present enhanced dielectric loss and weakened magnetic loss (resonance-antiresonance behavior) associated with the permeability-to-permittivity transformation at a specific frequency region. All the milled samples exhibit prominently continuous dual-absorption peaks, which substantially broaden the effective absorption bandwidth. The samples with milling time of 16 h exhibit optimal EMW absorbing performance, where the RLmin value of 65.2 dB is achieved at 14.4 GHz with a thickness of 2.90 mm. The present work further extends the domain of functional behavior for Heusler-type NiMn-based alloys. It is demonstrated that Heusler type NiMn-based alloys could be a competitive candidate for EMW absorption applications. Acknowledgment This work was supported by the National Natural Science Foundation of China (Grant Nos. 51571056, 51771048), the Fundamental Research Funds for the Central Universities of China (Grant Nos. N180204013, N170908001 and N170904001), the Liaoning Revitalization Talents Program (Grant No. XLYC1802023) and the Research Funds for Innovation Talents in Universities and Colleges of Liaoning Province (Grant No. LR2016003). References [1] X.F. Liu, Y.X. Chen, X.R. Cui, M. Zeng, R.H. Yu, G.S. Wang, J. Mater. Chem. 3 (2015) 12197e12204. [2] P.Y. Liu, L.M. Wang, B. Cao, L.C. Li, K.L. Zhang, X.M. Bian, Z.L. Hou, J. Mater. Chem. C 5 (2017) 6745e6754. [3] N. Zhang, Y. Huang, M. Zong, X. Ding, S.P. Li, M.Y. Wang, Chem. Eng. J. 308 (2017) 214e221. [4] H.F. Li, J. Wang, Y.H. Huang, X.Q. Yan, J.J. Qi, J. Liu, Y. Zhang, Mater. Sci. Eng. B 175 (2010) 81e85. [5] D.P. Sun, Q. Zou, G.Q. Qian, C. Sun, W. Jiang, F.S. Li, Acta Mater. 61 (2013) 5829e5834. [6] T.T. Chen, F. Deng, J. Zhu, C.F. Chen, G.B. Sun, S.L. Ma, X.J. Yang, J. Mater. Chem. 22 (2012) 15190e15197. [7] X.F. Liu, X.Y. Nie, R.H. Yu, H.B. Feng, Chem. Eng. J. 334 (2018) 153e161. [8] X. Wang, R.Z. Gong, P.G. Li, L.Y. Liu, W.M. Cheng, Mater. Sci. Eng. A 466 (2007) 178e182. vet-Vincent, F. Fie vet, Adv. Mater. 10 [9] P. Toneguzzo, G. Viau, O. Acher, F. Fie (1998) 1032e1035. [10] V.F. Meshcheryakov, Y.K. Fetisov, A.A. Stashkevich, G. Viau, J. Appl. Phys. 104 (2008), 063910. [11] C. Liu, Y. Yuan, J.T. Jiang, Y.X. Gong, L. Zhen, J. Magn. Magn. Mater. 395 (2015) 152e158. [12] S.J. Yan, L. Zhen, C.Y. Xu, J.T. Jiang, W.Z. Shao, J.K. Tang, J. Magn. Magn. Mater. 323 (2011) 515e520. [13] Q.R. Jiang, H.L. Li, Z.M. Cao, H. Li, Q.X. Wang, Z.Y. Jiang, Q. Kuang, Z.X. Xie, J. Alloy. Comp. 726 (2017) 1255e1261. [14] Z.X. Yu, N. Zhang, Z.P. Yao, X.J. Han, Z.H. Jiang, J. Mater. Chem. 1 (2013) 12462e12470. [15] L.N. Huang, X.F. Liu, D. Chuai, Y.X. Chen, R.H. Yu, Sci. Rep. 6 (2016) 35377. [16] S. Pandey, S. Vyzulin, A. Quetz, A. Aryal, I. Dubenko, A. Granovsky, S. Stadler, N. Ali, AIP Adv. 8 (2018), 056707. [17] J. Feng, Z.B. Li, Y.S. Jia, B. Yang, S.J. Liu, X. Zhao, L.W. Li, L. Zuo, J. Mater. Sci. 53 (2018) 11779e17790. [18] K. Ullakko, J.K. Huang, C. Kantner, R.C. O’Handley, V.V. Kokorin, Appl. Phys.
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Please cite this article as: J. Feng et al., Enhanced electromagnetic wave absorption properties of Ni2MnGa microparticles due to continuous dual-absorption peaks, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152588